In this research project, the Slug Mucosal Irritation (SMI) assay was applied to predict nasal discomfort, investigating the correlation between responses in slugs and humans. Several SMI experiments and a Human Nose Irritation Test (HNIT) were performed with five NaCl solutions (0.4%, 1.3%, 2.6%, 5.4% and 10.4%) and two benzalkonium chloride solutions (BAC 0.02% and BAC 0.05%). In the HNIT, subjective evaluation of clinical discomfort was performed by 24 participants at several time points. Analyzes reveal that (1) a significant positive association existed between immediate stinging reaction reported by the participants and the mean total mucus production of the slugs (Spearman's Rank correlation=0.963, p<0.001); (2) NaCl 0.4% was best tolerated in both tests; (3) a concentration-response effect was observed for NaCl and BAC solutions; (4) NaCl 10.4% induced the highest mucus production in the slugs and received higher sting scores for immediate discomfort in the HNIT; (5) stinging sensations decreased rapidly in time and (6) based on these results a new classification prediction model for nasal applications was established. In conclusion, the SMI assay is a promising evaluation method for clinical nasal discomfort. Screening (prototype) formulations with this assay allows formula optimization prior to a clinical trial.
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